The invention relates to a random number generating circuit, semiconductor integrated circuit, IC card and information terminal device. In particular, the invention relates to a random number generating circuit, semiconductor integrated circuit, IC card and information terminal device capable of generating high-quality digital random number signals at high rates.
In recent years, sophisticated physical random numbers have been increasingly needed in information security, simulation and other areas. In particular, from the viewpoint of ensuring security in mobile devices such as IC cards and cellular phones, a small-size random number circuit is required which can generate high-quality random numbers at high rates. However, in physical random number generators, there has often been a tradeoff between the rate of generating random numbers and their quality. It has been a problem that the generating rate is forced to be lowered to ensure a sufficient quality of random numbers with a small-size physical random number circuit.
A solution to the problem is, for example, to provide a plurality of random number circuits, each outputting 1-bit physical random numbers. The plurality of outputs are sequentially read out, thereby being regarded as a 1-bit random number sequence. However, this solution has problems that it is difficult to provide a plurality of physical random number circuits having similar characteristics, and that the circuit scale increases.
Another solution is to store data in a memory and rapidly read it out when needed. However, this solution has problems that the frequency of using random numbers is limited in order to ensure sufficient time for storing the random number data. To avoid this problem, a stored random number sequence is operated with a slowly generated random number sequence to form a new random number sequence which is stored back in the memory (Japanese Laid-Open Patent Application (Kokai) 2001-290634). While this solution overcomes the problem of the generating rate, it has a problem that the random numbers exhibit periodicity because the information of the same random numbers is repeatedly used.
As described above, in the conventional art, it is not easy to generate high-quality random numbers at high rates with a small-scale circuit.